Any swimming pool, spa or other manmade body of water using a recirculation pump poses the risk of drowning or incapacitation to a person drawn to the suction intake opening. There are numerous documented events of drownings or injuries caused by persons being drawn to a suction intake opening and becoming unable to escape the suction caused by the pump.
Most recirculation pumps operate with 120 (or 220) volt, single phase electric motors. When these motors are actuated, the attached pumps pull water from the pool and recirculate the water back into the pool. In the recirculation fluid flow circuit there may be filters, heaters and/or other devices through which the water passes. A negative pressure (suction) is generated on the suction side of the pump, and a positive pressure is generated on the discharge side of the pump.
Most common recirculation pump electrical installations consist of a motor control center with circuit breakers feeding electrical current to a timing device having a power relay. The timing device and power relay cooperate to turn the electric pump motor on and off on a predetermined schedule. There will normally be two 120 volt lines (L1 and L2) from the motor control center to the timing device. There will normally be two lines from the timing device (Load 1 and Load 2) to the electrical motor. There should also be a grounding wire (G) grounding the various pieces of equipment. There may or may not be a neutral wire (N). If there are auxiliary devices such as filters these are normally equipped with a pressure gauge for monitoring the water pressure, or pressure differential, at or across said devices.
U.S. Pat. No. 4,620,835 (the '835 patent) discloses an example of a system for protecting a swimming pool electrical motor in the event of a blockage. However, the system of the '835 patent is representative of the shortcomings of various prior art pump protection systems, in that they are not designed with the safety of pool users in mind. For instance, the '835 patent utilizes a manual override to disable the automatic shutoff system when the recirculation pump is coming up to pressure and when the system in being shut down. Also, pneumatic means are utilized for protecting the pump that, were a blockage caused as a result of pool user entrapment, may allow re-established of pump suction before the user is able to completely disengage him- or herself.